Exam 1 ~Modules 1-4

How many amino acids are hydrophilic with a negative charge?

2

How many different amino acids are there?

20

How many amino acids are hydrophilic with a positive charge?

3

What protein is the most plentiful in egg whites? At what temperature does it denature?

54% of proteins in egg whites is Ovalbumin. It denatures at a temperature of 77°C

How many amino acids are hydrophilic with a neutral charge?

7

How many amino acids are hydrophobic?

8

When densely packed, starch molecules can be crystalline or amorphous. Compare and contrast these two types of structures.

A crystalline structure is a solid in which the molecules are arranged in an orderly fashion. Amorphous structure is a solid in which the molecules are arranged randomly. It is disordered.

Describe the structure of a salt crystal. State the type of bond that holds the crystal together. Explain why these bonds are broken when a salt crystal is placed in water.

A salt crystal is a lattice of alternating chloride (Cl) and sodium (Na) atoms. It is held together by ionic bonds because the chlorine atoms are MUCH more electronegative than the sodium atoms. When a salt crystal is placed in water, the ionic bonds break as the sodium ions (Na+) and chloride ions (Cl-) form hydrogen bonds with the surrounding water molecules.

Describe what is happening to a starch grain in a wet potato when being heated

A starch granule is composed of many starch molecules. When a starch granule is heated in the presence of water, it swells. In particular, the heating process breaks bonds between starch molecules and allows water to seep in between the molecules.

The graph below shows the viscosity of egg yolk at different heating temperatures. Using the graph, answer the following questions: A. As an egg yolk is held at a constant temperature of 63°C, how does the viscosity change? B. If the egg is being held at a constant temperature, why would the viscosity continue to change? C. What is the impact of increasing the temperature on viscosity? How does cooking an egg yolk at 66°C differ from 63°C?

A: The viscosity steadily increases with time. B: The proteins in the egg yolk do not all denature at the same time. It is a statistical event. However, once a protein denatures, it does go back to its native structure. Thus, over time, more and more proteins denature. As more proteins denture, the viscosity increases. C: An egg yolk at a higher temperature will have proteins that denture faster. Since the proteins denture faster, theviscosity should increase more quickly, just like what is shown in the graph.

Describe the shape and number of glucose residues in the molecule amylopectin

Amylopectin is a highly branched network of glucose molecules. It contains between 10,000 and 100,000 glucose residues in a single molecule.

Describe the shape and number of glucose residues in the molecule amylose

Amylose is a linear chain of glucose molecules and contains between 1,000 and 10,000 glucose residues (i.e. molecules).

What is an Onsen egg? Explain what is happening to the proteins in an Onsen egg.

An Onsen egg is an egg cooked in a hot spring (the tradition comes from Japan). The hot springs are just warm enough to denature proteins in eggs slowly. Thus, by leaving the egg in the hot spring for an extended time, the proteins denature and the egg inside the shell resembles that of a poached egg

Describe the difference between water molecules in a cold cup of water and a hot cup of water.

As the temperature of the water increases, the kinetic energy of the water molecules also increases. Thus, the water molecules in the hot cup of water will be moving more than the water molecules in the cold cup of water.

Compare and contrast the curve for fungus growth and bacterial growth. If a food had a water activity of 0.82 is it at risk for fungus growth? How about bacterial growth?

At 0.82 water activity, the rate of bacterial growth is very slow. At 0.82 water activity, fungus growth is present. A food at 0.82 water activity would be at risk for fungus growth but not bacterial growth.

What is the difference between baking soda and baking powder?

Baking soda is a base. When it is combined with an acid, CO2 is generated. Baking powder has baking soda in it. It also has acid in the form of crystals that melt when heated.

Amino acids containing a sulfur atom are particularly important to the behavior of proteins. Why?

Because it has helps the denatured proteins bond with their side groups of cysteine during in a process called coagulation.

Describe why water is good at dissolving other substances.

Because water forms hydrogen bonds with itself and other substances that have some electrical polarity in the distribution of positive and negative electrical charges

What are three ways to inflate a dough with air?

Chemical Leavening Biological Leavening Mechanical Leavening

Explain what happens when a protein coagulates.

Coagulates happens when the molecules are extended, and their side groups begin to bond with each other.

Describe the structure of collagen before it is heated. Then describe what happens to collagen if it is heated for a short time AND a long time

Collagen (a protein) has a triple helical structure. When heated, it denatures, and the helical structure is lost. However, the individual collagen molecules remain intact. After prolonged heating, the collagen undergo hydrolysis and the long collagen molecule is broken up into smaller pieces (peptides). These smaller pieces are called gelatin.

How are covalent bonds formed?

Covalent bond is formed between the hydrogen and oxygen atom of an individual water molecule.

What role does the amino acid Cysteine play in the development of gluten?

Cysteine amino acids in the proteins glutenin and gliadin contribute to bonds between proteins. In particular, two cysteine amino acids can form a bond called a disulfide bridge.

Explain what happens when a protein denatures.

Denature happens when there is breaking of the bonds that maintain the molecule's folded shape.

The table below represents six different types of triglycerides. Each triglyceride is composed of three fatty acids. Long lines represent saturated fatty acids with 18 carbon atoms (labeled S) and short lines represent saturated fatty acids with 16 carbon atoms (labeled P). The column on the right is the melting temperature for the different triglycerides. (The comma instead of a decimal is a European thing.)

Different melting temperatures correspond to different attractions between molecules in the solid. Since different shape triglycerides will result in different attractions, it makes sense that the melting temperature will also differ. The SSS triglyceride has the longest carbon backbones and a symmetrical shape making it easy to pack into a crystal structure. Thus, attraction between the SSS will be large and therefore result in a high melting temperature.

When dough is stretched out, it often returns (at least partly) to its original shape. This represents elastic behavior. Explain, at the molecular level, why the dough behaves this way.

Dough is elastic because the gluten molecules are coiled and have many kinks in them. When a mass of dough is stretched, the kinks are straightened out, the coils extended, and the proteins get longer. When the stretching tension Is released, many of the kinks and coils re-from, the protein mass shortens, and the dough shrinks back toward its original shape.

When do starch granules in dough swell with water?

During the baking of bread and cakes, starch granules absorb water, swell and set to from the rigid bulk of the walls that surround the bubbles of carbon dioxide.

What is the impact of fats on gluten formation?

Fats weaken gluten by bonding to the hydrophobic amino acids along the protein chains and so preventing them from bonding to each other.

What happens in the 'gelation range' of a starch?

Gelation range is the temperature that causes the starch granules to lose their shape. At 120-140°F, the granules suddenly lose their organized structure and absorb a lot of water then become amorphous networks of starch and water intermingled

A dough typically has less water in it (more flour) than a batter. However, a well kneaded dough doesn't appear wet. How are the water molecules bound up in the dough? What are they bound to?

Generally, dough contains more flour than water which cause it to be stiff enough to be manipulated by hand. All the water is bound to the gluten proteins and to the surfaces of the starch granules, which are embedded in the semisolid gluten-water matrix.

What is a globular protein? In what food are globular proteins found?

Globular protein compact elaborately folded molecules. They are found in eggs

Explain the significance of specific heat capacity in waiting (and waiting and waiting) for a pot of water to boil

Heat capacity quantifies the amount of energy needed to raise the temperature of a substance. Water has an exceptionally large heat capacity and thus takes a long time to heat up. Water takes a lot of energy to change its temperature.

How are hydrogen bonds formed?

Hydrogen bond is formed between polar water molecules. It would form between the hydrogen of one molecule and the oxygen of another water molecule.

Compare and contrast hydrogen bonds and covalent bonds.

Hydrogen bonds are much weaker and take less energy to break than covalent bonds which are strong and harder to break apart

What does hydrophilic and hydrophobic mean?

Hydrophilic means that they are not scared of water, they can bond with it while Hydrophobic means that they fear water and hide away from it.

Describe what is happening at the molecular level when ice melts into liquid water.

Ice is a crystal. When water is frozen (ice) the water molecules are fixed on lattice sites. The crystal is being held together with hydrogen bonds. The molecules are still moving (jiggling) but they don't leave their lattice sites until it reaches a certain temperature to break bonds.

Melted chocolate that is then cooled in the refrigerator can come out with a dull sheen and is soft instead of snappy. The chart below shows the melting temperature of the six different crystal structures (called forms). Using the chart, explain what is happening when melted chocolate is cooled quickly.

If it is cooled quickly, then the chocolate is going to be more dull with poor temperature. It is not going to have the loud snap that it's supposed to have.

What proteins are denatured in medium-rare steak?

In a medium-rare steak, the main protein that contracts is myosin

Egg white begins to thicken at 145ºF/63ºC and becomes a tender solid when it reaches 150ºF/65ºC. Which protein is this solidification due to?

It is due to Ovotransferrin

Describe the structure of kneaded dough.

Kneaded dough is composed of a gluten network with starch granules embedded in the network. The process of kneading bonds the proteins glutenin and gliadin into elastic sheets within the dough.

Why is latent heat important to steaming? Describe the source of this energy.

Latent Heat Vaporization is the amount of heat required to change water to steam. The phase change of steam requires a tremendous amount of additional energy. The ability of steam to carry large amounts of thermal energy, is what makes latent heat so important.

Why can a smaller amount of potato starch thicken better than a small amount of wheat or corn starch? Make sure to use the word amylose in your explanation.

Long amylose molecules are better at thickening because they coil up into long helical structures when dissolved in water, but they retain their basically linear shape. Their elongation makes it very likely that one chain will wrap or knock itself around another or into a granule which abords a lot of water.

Why does white rice become hard when cooled in the refrigerator? Explain what is happening at the molecular level.

Long-grain white rice has a relatively large fraction of amylose molecules. Amylose molecules are long linear chains that back together densely when cooled. Thus, when rice is cooled, the amylose molecules in the rice reconfigure and pack densely leading to the texture of the rice becoming hard. This is called retrogradation.

The images below show a polymer (like a protein) in a good solvent and a poor solvent. The polymer is represented by a series of red dots that are connected. The solvent (like water) is represented with blue dots. Which cartoon, A or B, represents a poor solvent for the polymer and why?

Option A is the poor solvent while Option B is the good solvent. Option B is hydrophilic and Option A is hydrophobic.

What percentage of water (water content) is our bodies, raw meat, and fruits and vegetables?

Our bodies are made up of 60% water content by weight Raw meat is about 75% water content Fruits and Vegetables has up to 95% water content

What are the three most common proteins found in eggs?

Ovalbumin, Ovotransferrin, Ovomucoid

Why are water molecules 'polar'?

Oxygen is more electronegative than hydrogen. Thus, when a covalent bond forms, the shared electrons are pulled more towards the oxygen than the hydrogen. This results in the molecule being polar. The overall charge is neutral, but it is more negatively charged near the oxygen and more positively charged near the hydrogen.

Below is a differential scanning calorimetry curve of sliced round beef created by heating the beef at a rate of 10°C/min. The two peaks correspond to proteins in the muscle fiber denaturing. Which protein leads to peak I? Which protein leads to peak II?

Peak I is due to the protein myosin, Peak II is due to the protein actin

What are polysaccharides? In your response, use the word 'polymer.'

Polysaccharides, include starch and cellulose. They are polymers of simple sugars that are monosaccharides linkd together. This means molecules are composed of numerous individual sugar units.

What percentage of flour is starch as compared to protein?

Proteins accounts for only 10% of flour weight and 70% starch.

Why is it important to let meat rest before cutting?

Resting allows water to settle in the steak because the liquid is bonding with the other proteins and becoming more solid. If you cut it right away all your juices will drip out, actin and myosin collagen form bonds to help squeeze out water but when you let it rest, they relax and allows water to go back into the muscle fibers and allows them to not leak out when you cut open you steak

What is the impact of salt on the gluten network? Why?

Salt greatly strengthens the gluten network. The electrically positive sodium and negative chlorine ions cluster around the few charged portions of the glutenin proteins, prevent those charged portions form repelling each other, and so allow the proteins to come closer to each other and bond more extensively.

Explain the difference in molecular structure between saturated and unsaturated fats.

Saturated fats can be easily packed together as it has all hydrogen atoms causing it to be a straight chain. They are also are more attracted to each other, while unsaturated fats are missing some hydrogen atoms that cause them to have kinks that prevents them from getting close. Unsaturated fats also can result in double bonds forming between carbon atoms.

Describe the changes of temperature of a block of ice continuously heated.

Section A: Ice is changing in temperature and getting warmer. Section B: Ice melts into liquid water. The temperature remains constant during this phase transition. Section C: Liquid water is changing in temperature and getting warmer. Section D: Liquid water is boiling and becoming water vapor. The temperature remains constant during this phase transition. Section E: Water vapor is changing in temperature and getting warmer.

What is sous-vide cooking? Why does it allow a chef more control than typical cooking methods?

Sous vide means under vacuum. However, today, sous vide cooking is recognized as cooking using a water bath with excellent temperature control. The fine temperature control allows a chef to choose what proteins are denatured and what proteins are not.

What is the benefit to cooking meat using the sous vide method rather than grilling? What issue arises when meat is cooked using the sous vide method?

Sous vide method allows for more uniform and gentle heating. This results in the protein network in the meat being denatured by a similar about everywhere. Thus, unlike the "bulls eye" texture of a grilled steak, a steak cooked using sous vide is much more uniform in texture. The water in a sous vide bath is kept at a fairly low temperature. Thus, the Maillard reaction doesn't occur onthe surface of the meat (which typically requires temperatures closer to 330°F). The lack of the Maillardreaction results in a lack of flavor molecules desired by the consumer. To put it another way, meat cooked viathe sous video method will not have a browned surface and therefore have less flavor molecules.

. What is a van der Waals bond? Why is it relevant for the study of fat molecules in the kitchen?

The Van Der Waals Bond is when fatty acids are attracted to each other via a weak bond that forms between nonpolar molecules.

You likely have heard of foods that are fats and foods that are oils. From a molecular point of view, what is the difference between them?

The difference is that at melting points food that are fats are solids while the food that are oils are liquids. The intermolecular forces between molecules in fats is stronger then oils.

The graph below is a differential scanning calorimetry curve for fresh egg whites. What do the different valleys represent? What do they tell you about the composition of egg whites?

The different valleys represent different types of proteins in the egg denaturing. Since there is more than one valley, that suggests there is more than one type of protein in egg whites.

Relationship between water content and water activity for a food at a fixed temperature can be split into 3 regions (I, II, and III). State the range of water activity values and describe the mobility of the water molecules, texture of the food, and food stability for REGION 1.

The first region (I) ranges from a water activity of 0— 0.35. It is identified as low water activity that has low water mobility but high stability. This region inhabits foods that have a dry and crisp texture. (Goldfish or chips)

How does the behavior of the proteins glutenin and gliadin differ when kneading dough?

The gluten of bread is both plastic and elastic, this means it will change its shape under pressure, yet it resists the pressure and goes back to its original shape when pressure is removed. Gluten plasticity results from the presence of the gliadin proteins because they are compact, they act like ball bearing allowing portions of glutenin's to slide past each other without bonding. Elasticity results from the kinked and coiled structure of the interconnected gluten proteins.

The images below show two different ways 4 triglycerides molecules could be arranged. Each image is a different phase of matter. State the phase of matter for each. Compare and contrast their structures.

The image on the left (A) shows the triglycerides as a liquid (i.e. an oil). They are more disordered. The image on the right (B) shows the triglycerides as a solid (i.e. a fat). They are more ordered.

In raw egg white, describe the structure of the proteins.

The proteins are long chains of amino acid. The protein in egg whites are globular proteins.

What is protein coagulation and why is it relevant for cooking eggs?

The proteins are pulled together and start to bond. This makes the eggs more opaque.

Relationship between water content and water activity for a food at a fixed temperature can be split into 3 regions (I, II, and III). State the range of water activity values and describe the mobility of the water molecules, texture of the food, and food stability for REGION 2.

The second region (II) ranges from a water activity of 0.35—0.75. It is identified as medium water activity that has medium water mobility but intermediate stability. This region inhabits foods that have a chewy and moist texture. (Nature valley crunch bars)

Describe the smoke point of a fat? What is it and what is happening at the molecular level?

The smoke point of a fat is the temperature where fats break down into visible gas from products. A smoke point, most fats start to decompose at temperature below the boiling point. The other active free fatty acid that remains in the food after the smoke point is damaging to the flavor of the food

Relationship between water content and water activity for a food at a fixed temperature can be split into 3 regions (I, II, and III). State the range of water activity values and describe the mobility of the water molecules, texture of the food, and food stability for REGION 3.

The third region (III) ranges from a water activity of 0.75—1.0. it is identified as high-water activity that has high water mobility but low stability. This region inhabits foods that have a soft and juicy texture. (Meats)

What is the thumb test? Explain why it works. Make sure to use the word proteins

The thumb test is a way of representing the texture of meat as it cooks. The pad of the thumb represents the texture of meat. By touching different figures to the tip of the thumb, the stiffness of the pad of the thumb changes. It gets stiff in a similar way as meat gets stiffer when cooked. The reason meats stiffen when cooked is that proteins (particularly myosin and actin) denature and coagulate. This results in a stronger network that increases the stiffness of the meat.

What two proteins in flour contribute to the development of gluten in dough?

The two proteins are Glutenin and Gliadin.

What happens to the water in egg whites when they are cooked?

The water is divided into countless little pockets in the protein network.

Often wood is used as a material to make a stirring spoon (for example to stir soup or a sauce in a pot). Why is wood preferred over aluminum? In your answer, discuss the role of conductivity.

Thermal conductivity is the rate at which heat can traverse through a substance. Wood has a low thermal conductivity. Aluminum has a high thermal conductivity. Thus, if stirring a hot liquid, heat (energy) will travel much faster up an aluminum spoon than a wood spoon.

The image below is of a fatty acid ester, common in canola oil. The two red balls represent oxygen atoms. What do the white and dark gray balls represent?

They represent fatty acid and glycerol backbone

The melting temperature of a saturated fatty acid and the length of the fatty acid (i.e. n is the number of carbon atoms in the fatty acid). Based on a graph that has a carbon chain of 0 where the line is going up as we go to the right of the graph, state the trend. In addition, explain the physics of the apparent trend.

This means that as the number of carbon atoms in the saturated fatty acid (n) increases, so does the melting degree.

The relationship between the melting temperature of an unsaturated fatty acid with a fixed length (18 carbon atoms) and the number of kinks (unsaturated) bonds in the structure (noted with the variable s). Based on a graph with a carbon chain of 18 and the line goes down as we go to the right of the graph, state the trend. In addition, explain the physics of the apparent trend.

This means that as the number of kinks (unsaturated fats) increases the melting degree decreases.

What is the difference between a cut tough of meat and a tender cut of meat?

Tough cuts of meat have more connective tissue (thus collagen) than tender cuts of meat

Describe the atomic structure of triglycerides and their relationship to fatty acids and glycerol. Based on the molecular composition, explain why fats are nonpolar.

Triglycerides is the structure of 3 fatty acids, the type of bonds formed between fatty acid and glycerol backbones. They are nonpolar because they cannot be dissolved in water.

What is Chemical Leavening?

Using baking soda with an acid or baking powder to cause a chemical reaction within the dough that creates CO2.

What is Biological Leavening?

Using yeast (microorganism) that digests sugars and creates gas in the dough.

The phenomenological property called 'water activity' is useful when thinking about food. What are the range of values for water activity? What do they mean? How is 'water activity' different from 'water content'?

Water content is the amount of water in a substance. Water activity is the amount of 'free' or 'available' water in a substance. Water activity ranges from 0 (no free water molecules) to 1 (a vast majority of the molecules are free)

Describe the atomic structure of a water molecule?

Water is composed of 3 atoms: one oxygen and two hydrogen. Each hydrogen atom forms a covalent bond with the oxygen atom.

A product consists of two 'zones': dough and fruit stuffing. The moisture content of the dough is 20% with a water activity 0.55. The moisture content of the fruit filling is 11% with a water activity of 0.70. Will water molecules flow from the dough to the fruit filling or from the fruit filling to the dough? Explain your reasoning.

Water molecules move from high water activity to low water activity. Water molecules would move from the fruit filling into the dough based on the water activity.

What is special about the temperature at which ice melts?

What is special about the melting temperature is that it represents the right amount of thermal energy (which is related to temperature) for the water molecules to break free of the bonds holding them in a crystal structure.

What does it mean to 'temper' chocolate? Why do chocolatiers temper chocolate?

When chocolate is tempered, it is held at a temperature above the melting temperature of unwanted (or undesirable) chocolate crystals but below the temperature that desirable crystals form. Thus, undesirable fat crystals melt and form desirable fat crystals. Chocolatiers temper chocolate so the fat crystals form desirable crystal structures. This results in chocolatethat has a desirable sheen, snap, shelf stability, and melting temperatures

State the two ions and the charge of each ion in salt. Describe the hydrate shell that surrounds the salt ions dissolved in water.

When salt dissolves in water, the ionic bonds break and positively charged sodium ions (Na+) and negatively charged chloride ions (Cl-) go into the water. The water molecules that surround the ions are held in place because of the hydrogen bonds. This is called the hydrate shell.

When salt is placed in water, what is happening on a molecular level.

When salt is placed in water the negatively charged part of the polar water molecules (oxygen) is attracted to the positive ion (Na)

What happens when starch is placed in warm water?

When starch is placed in warm enough water the starch granules slowly absorb about 30% of their own weight and they simply sink to the bottom of the pot and sit there, but when the water gets warm enough the energy in its molecules is enough to disrupt the weaker regions of the granule. The granules then absorb more water and swell up, thereby putting greater and greater stress on the stronger/more organized granule regions.

Describe the process of sugar (sucrose) molecules dissolving in water and describe why polar molecules like sugar dissolve in water?

When sugar crystals are placed in water, the surrounding water molecules can form strong hydrogen bonds with the sugar molecules. This process breaks the bonds between the sugar molecules and allows them to dissolve into the water. A sugar molecule (like sucrose) is a polar molecule that is attracted to other sugar molecules. This attraction leads to sugar forming a crystal structure.

Why does ice melt at a particular temperature?

When water melts, the water molecules have enough energy to jiggle free of their lattice sites. In particular, at the melting temperature, the water molecules have enough thermal energy to break the hydrogen bonds holding them in their lattice positions. The water molecules are then free to move around and thus are liquid water.

What is Mechanical Leavening?

Whipping air into the dough. Some air is also incorporated into the dough in the kneading process.

Describe the state of matter for a gas

a fluid and dispersed group of atoms or molecules.

Describe the state of matter for a liquid

a loosely bonded, fluid mass of atoms or molecules

What percentage of egg whites is water?

about 90%

Describe how frozen water damages the cells in raw plant and animal tissues.

due to the even distribution of hydrogen bonds, more space is required in between molecules. Water expands when frozen and animal tissue gets damaged and ruptures the cell membrane

Describe the state of matter for a glassy solid

masses of atoms or molecules that have bonded to each other in a random arrangement.

Describe the states of matter for a crystalline solid

molecules bonded together in highly ordered, regular arrays.

Conduction is a type of heat transfer that......

the transfer of thermal energy exchanged through collisions Ex: the process of heating a pan on a stove. The heat from the burner transfers directly to the surface of the pan

Radiation is a type of heat transfer that......

transfer of thermal energy by electromagnetic radiation, where heat and light waves strike and penetrate your food. No contact needed! Ex: Roasting a marshmallow over a campfire.

Convection is a type of heat transfer that......

transfer of thermal energy by movement of molecules in a fluid from a warm region to a cold region Ex: Running water over frozen food, which transfers heat into the food to that is more quickly

What does it means to be a polar molecular?

when an entity contains two distinct and opposite poles that can either attract or repel each other

What are some of the challenges of making gluten-free pizza?

• Loss of chew due to diminished gluten network. • Loss of air in dough due to diminished gluten network. • Loss of browning due to lack of gluten proteins. • Loss of water do to lack for gluten network that water clings to